1. Field of the Invention
The invention relates to an apparatus for recording and/or reproducing information on an information carrier comprising
a head for reading and/or writing information from/on the information carrier, PA1 a rotatable member for moving the head and the information carrier relative to each other, PA1 a bearing for supporting said rotatable member relative to a frame so as to allow rotation of the rotatable member round an axis of rotation, PA1 a ground system comprising an electrical coupling between the rotatable member and a fixed terminal to limit static charging of the rotatable member, PA1 the bearing comprising bearing surfaces co-operating with each other for positioning the rotatable member in axial direction relative to the frame. PA1 during rotation of the rotatable member said bearing surfaces are in contact with each other, PA1 at least one of the bearing surfaces comprises tungsten carbide and that PA1 said electrical coupling between the rotatable member and the frame is formed by the contacting bearing surfaces. With these measures two functions can be fulfilled with one pair of surfaces. One of these functions is supporting the rotatable member in the axial direction. The other function is providing an electrical coupling between the rotatable member and the frame. In the known apparatus a fluid is pumped between the co-operating surfaces of the bearing so that the bearing surfaces are not in contact with each other, which results in a poor electrical coupling. The electrical coupling is instead obtained by a carbon element contacting a metal surface. However, carbon is not well suited to form a bearing because it has high wear. Also, it has been found that most hard materials do not result in a satisfactory ground system. Surprisingly, it has been found that with the measures according to the invention, the static charge on the rotatable member is limited such that spark discharges are counteracted in a satisfactory way and at the same time the bearing has a low wear. Due to this double function of the bearing, the ground spring can be dispensed with and the sound level produced by the apparatus is reduced.
2. Description of the Related Art
Such an apparatus is known from U.S. Pat. No. 5,019,926. The known apparatus comprises a magnetic-head drum system comprising a lower drum which is fixedly connected to a frame and an upper drum carrying magnetic heads. The tipper drum is supported by a shaft which is fixedly connected to the lower drum and the upper drum is rotatable round an axis of rotation defined by the shaft. The shaft is formed with pump grooves to form a radial helical-groove bearing which supports the upper drum in the radial direction. At the upper end of the shaft a thrust-bearing plate is arranged which is also formed with pump grooves and which is connected to the upper drum. The upper end of the shaft and the thrust-bearing plate form an axial helical-groove bearing to position the upper drum in the axial direction relative to the lower drum. Further, the known apparatus comprises a bridge construction which carries a ground spring which near its free end is connected to a pressure member. The spring presses the pressure member against a surface of the thrust-bearing member, which surface is opposite the bearing surface facing the shaft. During rotation of the upper drum the pressure member and the thrust-bearing plate are in sliding contact thereby enabling static charge built up oil the upper drum to be discharged via the ground spring.
A disadvantage of the known apparatus is that the sliding contact between the pressure member and the thrust-bearing plate cause vibrations in the ground spring which contribute to the sound level produced by the apparatus and ineffective contact quality because of a limited contact press force.